1. Field of the Invention
The present invention relates to organic electroluminescent elements which include one or more thin films (hereinafter referred to as an organic functional layer) including a light-emitting layer formed of an organic compound material that exhibits electroluminescence (hereinafter referred to as the EL) for emitting light by the injection of current. More particularly, the present invention relates to an organic EL display panel having a plurality of the organic EL elements formed on a resin substrate.
2. Description of the Related Art
An organic EL element has an anodic transparent electrode, an organic functional layer, and a cathodic metal electrode, which are sequentially deposited on a transparent substrate. For example, the organic functional layer can be formed in a three-layer structure which includes a single light-emitting layer or an organic hole transport layer, a light-emitting layer, and an organic electron transport layer or in a two-layer structure which includes an organic hole transport layer and a light-emitting layer. Alternatively, the organic functional layer can be a layered body with an electron or a hole injection layer or a carrier block layer which is inserted in between suitable layers of these structures.
For example, an organic EL display panel of a matrix type or having a predetermined light-emitting pattern is conventionally known as employs a plurality of organic EL elements.
It has been suggested to employ transparent resin or plastics as the transparent substrate of the organic EL display panel. On the other hand, the organic EL display panel has a problem of developing non-light-emitting portions or so-called dark spots when exposed to the atmosphere. In particular, the interface between the cathodic layer and the organic functional layer of an organic EL element is susceptible to deterioration in property caused by moisture. When the interface is exposed to moisture in the air, a chemical reaction occurs to cause a separation between the organic functional layer and the cathode, leading to the dark spot.
When substrates or films of resin are employed for displays such as LCDs or for food packaging, deposited thereon is a barrier film acting as an effective barrier to oxygen and moisture. In particular, for a substrate of resin for use with displays, a barrier film formed of silicon oxide (SiO2 or SiOx (x=1 to 2)) deposited by evaporation or sputtering is employed from the viewpoints of transparency and resistance to moisture.
Even for an organic EL element fabricated on a substrate of resin, it is necessary to provide the element with a film acting as a barrier to moisture in order to preserve the element in a good state. Conventionally, a moisture barrier film is provided between the organic EL element and the resin substrate; however, there is a problem in this structure that moisture enters the organic functional layer of the element from the surface of the resin substrate around the element.
Films such as SiO2 or SiOx deposited by evaporation or sputtering do not act as an effective barrier (to moisture) enough to prevent the organic EL element from being deteriorated. In addition, it is possible to obtain a film acting as a highly effective barrier to moisture by employing a film of SiNx (where x is an atomic number ratio) deposited by sputtering. However, the film is colored and thus has bad transparency. Moreover, high stress occurs in the film leading to deflection of the substrate or cracks in the film, and thus no practical applicability has been provided by the film.